Methods for depositing tungsten after surface treatment

ABSTRACT

In one embodiment, a method for forming a tungsten-containing material on a substrate is provided which includes positioning a substrate containing a metal nitride barrier layer within a process chamber and exposing the substrate to a reagent gas containing diborane to form a reagent layer on the metal nitride barrier layer. The method further provides exposing the substrate sequentially to a tungsten precursor and a reductant to form a nucleation layer during an atomic layer deposition (ALD) process and subsequently depositing a bulk layer over the nucleation layer. The bulk layer may contain copper, but generally contains tungsten deposited by a chemical vapor deposition (CVD) process. In some examples, the bulk layer may be used to fill apertures within the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/130,515(APPM/004349.C1), filed May 17, 2005, and issued as U.S. Pat. No.7,238,552, which is a continuation of U.S. Ser. No. 10/196,514(APPM/004349), filed Jul. 15, 2002, and issued as U.S. Pat. No.6,936,538, which claims benefit of U.S. Ser. No. 60/305,765(APPM/004349L), filed Jul. 16, 2001, which are herein incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to the processing of semiconductorsubstrates. More particularly, embodiments of the invention relate toimprovements in the process of depositing refractory metal layers onsemiconductor substrates.

2. Description of the Related Art

The semiconductor processing industry continues to strive for largerproduction yields while increasing the uniformity of layers deposited onsubstrates having larger surface areas. These same factors incombination with new materials also provide higher density of circuitsper unit area of the substrate. As circuit density increases, the needfor greater uniformity and process control regarding layer thicknessrises. As a result, various technologies have been developed to depositlayers on substrates in a cost-effective manner, while maintainingcontrol over the characteristics of the layer. Chemical vapor deposition(CVD) is one of the most common deposition processes employed fordepositing layers on a substrate. CVD is a flux-dependent depositiontechnique that requires precise control of the substrate temperature andprecursors introduced into the processing chamber in order to produce adesired layer of uniform thickness. These requirements become morecritical as substrate size increases (e.g., from 200 mm diametersubstrates to 300 mm substrates), creating a need for more complexity inchamber design and gas flow technique to maintain adequate uniformity.

A variant of CVD that demonstrates superior step coverage compared toCVD, is atomic layer deposition (ALD). ALD is based upon atomic layerepitaxy (ALE) that was employed originally to fabricateelectroluminescent displays. ALD employs chemisorption to deposit asaturated monolayer of reactive precursor molecules on a substratesurface by alternating pulses of an appropriate reactive precursor intoa deposition chamber. Each injection of a reactive precursor isseparated by an inert gas purge to provide an adsorbed atomic layer topreviously deposited layers to form a uniform layer on the substrate.The cycle is repeated to form the layer to a desired thickness. Adrawback with ALD techniques is that the deposition rate is much lowerthan typical CVD techniques by at least one order of magnitude.

Formation of film layers at a high deposition rate while providingadequate step coverage are conflicting characteristics oftennecessitating sacrificing one to obtain the other. This conflict is trueparticularly when refractory metal layers are deposited to coverapertures or vias during formation of contacts that interconnectadjacent metallic layers separated by dielectric layers. Historically,CVD techniques have been employed to deposit conductive material such asrefractory metals in order to inexpensively and quickly fill vias. Dueto the increasing density of semiconductor circuitry, tungsten has beenused based upon superior step coverage to fill these high aspect ratiostructures. As a result, deposition of tungsten employing CVD techniquesenjoys wide application in semiconductor processing due to the highthroughput of the process and good step coverage.

Depositing tungsten by traditional CVD methods, however, is attendantwith several disadvantages. For example, blanket deposition of atungsten layer on a semiconductor wafer is time-consuming attemperatures below 400° C. The deposition rate of tungsten may beimproved by increasing the deposition temperature between approximately500° C. to 550° C. However, temperatures in this higher range maycompromise the structural and operational integrity of the underlyingportions of the integrated circuit being formed. Use of tungsten hasalso complicated photolithography steps during the manufacturing processas it results in a relatively rough surface having a reflectivity of 20%or less than that of a silicon substrate. Finally, tungsten has provendifficult to uniformly deposit on a substrate. Variance in filmthickness of greater than 1% has been shown, thereby causing poorcontrol of the resistivity of the layer. Several prior attempts toovercome the aforementioned drawbacks have been attempted.

For example, in U.S. Pat. No. 5,028,565 to Chang et al., which isassigned to the assignee of the present invention, a method is disclosedto improve, inter alia, uniformity of tungsten layers by varying thedeposition chemistry. The method includes, in pertinent part, formationof a nucleation layer over an intermediate barrier layer beforedepositing the tungsten layer via bulk deposition. The nucleation layeris formed from a gaseous mixture of tungsten hexafluoride, hydrogen,silane and argon. The nucleation layer is described as providing a layerof growth sites to promote uniform deposition of a tungsten layerthereon. The benefits provided by the nucleation layer are described asbeing dependent upon the barrier layer present. For example, theuniformity of a tungsten layer is improved by as much as 15% when formedon a titanium nitride barrier layer. The benefits provided by thenucleation layer are not as pronounced if the barrier layer formed fromsputtered tungsten or sputtered titanium tungsten.

A need exists, therefore, to provide techniques to improve thecharacteristics of refractory metal layers deposited on semiconductorsubstrates.

SUMMARY OF THE INVENTION

A method and system to form a refractory metal layer over a substrateincludes introduction of a reductant, such as PH₃ or B₂H₆, followed byintroduction of a tungsten containing compound, such as WF₆, to form atungsten layer. It is believed that the reductant reduces the fluorinecontent of the tungsten layer while improving the step coverage andresistivity of the tungsten layer. It is believed that the improvedcharacteristics of the tungsten film are attributable to the chemicalaffinity between the reductants and the tungsten containing compound.The chemical affinity provides better surface mobility of the adsorbedchemical species and better reduction of WF₆ at the nucleation stage ofthe tungsten layer.

The method can further include sequentially introducing a reductant,such as PH₃ or B₂H₆, and a tungsten containing compound to deposit atungsten layer. The formed tungsten layer can be used as a nucleationlayer followed by bulk deposition of a tungsten layer utilizing standardCVD techniques. Alternatively, the formed tungsten layer can be used tofill an aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a semiconductorprocessing system in accordance with the present invention.

FIG. 2 is a schematic cross-sectional view of one embodiment of theprocessing chambers shown above in FIG. 1.

FIG. 3 is a schematic cross-sectional view of a substrate showing onepossible mechanism of adsorption of a reductant over a substrate duringsequential deposition.

FIG. 4 is a schematic cross-sectional view of a substrate showing onepossible mechanism of adsorption of a refractory metal containingcompound over the substrate after introduction of the reductant.

FIG. 5 is a graphical representation showing the concentration of gasespresent in a processing chamber, such as processing chamber as shownabove in FIG. 2.

FIG. 6 is a graphical representation showing the relationship betweenthe number of ALD cycles and the thickness of a layer formed on asubstrate employing sequential deposition techniques, in accordance withthe present invention.

FIG. 7 is a graphical representation showing the relationship betweenthe number of sequential deposition cycles and the resistivity of alayer formed on a substrate employing sequential deposition techniques,in accordance with the present invention.

FIG. 8 is a graphical representation showing the relationship betweenthe deposition rate of a layer formed on a substrate employingsequential deposition techniques and the temperature of the substrate.

FIG. 9 is a graphical representation showing the relationship betweenthe resistivity of a layer formed on a substrate employing sequentialdeposition techniques and the temperature of the substrate, inaccordance with the present invention.

FIG. 10 is a schematic cross-sectional view of one embodiment of apatterned substrate having a nucleation layer formed thereon employingsequential deposition techniques, in accordance with the presentinvention.

FIG. 11 is a schematic cross-sectional view of one embodiment of thesubstrate, shown above in FIG. 10, with a refractory metal layer formedatop of the nucleation layer employing CVD, in accordance with thepresent invention.

FIG. 12 is a graphical representation showing the concentration of gasespresent in a processing chamber, such as the processing chamber as shownabove in FIG. 2, in accordance with an alternative embodiment of thepresent invention.

FIG. 13 is a graphical representation showing the concentration of gasespresent in a processing chamber, such as processing chamber as shownabove in FIG. 2, in accordance with an alternative embodiment of thepresent invention.

FIG. 14 is a graphical representation showing the fluorine contentversus depth of a refractory metal layer formed on a substrate employingALD, either Ar or N₂ being a carrier gas.

FIG. 15 is a graphical representation showing the fluorine contentversus depth of a refractory metal layer formed on a substrate employingALD with H₂ being a carrier gas.

FIG. 16 is a schematic cross-sectional view of one embodiment of asubstrate shown above in FIGS. 3 and 4 upon which a layer of either PH₃or B₂H₆ is disposed between a substrate and a tungsten layer, inaccordance with one embodiment of the present invention.

FIG. 17 is a graphical representation showing the concentration of gasespresent in a processing chamber, such as processing chamber as shownabove in FIG. 2, in accordance with one embodiment of the presentinvention.

FIG. 18 is a schematic cross-sectional view of one embodiment of asubstrate shown above in FIGS. 3 and 4 in which a titanium-containinglayer is deposited between a substrate and a layer of either PH₃ orB₂H₆, in accordance with the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary wafer processing system includes oneor more processing chambers 12 and 14 disposed in a common work area 16surrounded by a wall 18. Processing chambers 12 and 14 are in datacommunication with a controller 22 that is connected to one or moremonitors, shown as 24 and 26. The monitors typically display commoninformation concerning the process associated with processing chambers12 and 14. One of the monitors 26 is mounted on wall 18, with theremaining monitor 24 being disposed in work area 16. Operational controlof processing chambers 12 and 14 may be achieved by the use of a lightpen, associated with one of the monitors 24 and 26, to communicate withcontroller 22. For example, light pen 28 is associated with monitor 24and facilitates communication with controller 22 through monitor 24.Light pen 39 facilitates communication with controller 22 throughmonitor 26.

Referring both to FIGS. 1 and 2, each of processing chambers 12 and 14includes a housing 30 having a base wall 32, a cover 34 disposedopposite to base wall 32, and a sidewall 36 extending therebetween.Housing 30 defines a chamber 37, and a pedestal 38 is disposed withinprocessing chamber 37 to support a substrate 42, such as a semiconductorwafer. Pedestal 38 may be mounted to move between cover 34 and base wall32, using a displacement mechanism (not shown), but the position thereofis typically fixed. Supplies of processing gases 39 a , 39 b and 39 care in fluid communication with processing chamber 37 via a showerhead40. Regulation of the flow of gases from supplies 39 a , 39 b and 39 cis effectuated via flow valves 41.

Depending on the specific process, substrate 42 may be heated to adesired temperature prior to layer deposition via a heater embeddedwithin pedestal 38. For example, pedestal 38 may be resistively heatedby applying an electric current from AC power supply 43 to heaterelement 44. Substrate 42 is, in turn, heated by pedestal 38, and can bemaintained within a desired process temperature range of, for example,about 20° C. to about 750° C. A temperature sensor 46, such as athermocouple, is also embedded in wafer support pedestal 38 to monitorthe temperature of pedestal 38 in a conventional manner. For example,the measured temperature may be used in a feedback loop to control theelectrical current applied to heater element 44 by power supply 43 suchthat the substrate temperature can be maintained or controlled at adesired temperature that is suitable for the particular processapplication. Optionally, pedestal 38 may be heated using radiant heat(not shown). A vacuum pump 48 is used to evacuate processing chamber 37and to help maintain the proper gas flows and pressure inside processingchamber 37.

Referring to FIGS. 1 and 2, one or both of processing chambers 12 and14, discussed above may operate to deposit refractory metal layers onthe substrate employing sequential deposition techniques. One example ofsequential deposition techniques in accordance with the presentinvention includes atomic layer deposition (ALD). The term “substrate”as used herein includes the substrate, such as semiconductor substratesand glass substrates, as well as layers formed thereover, such asdielectric layers (e.g., SiO₂) and barrier layers (e.g., titanium,titanium nitride and the like).

Not wishing to be bound by theory, FIG. 3 is a schematic cross-sectionalview of a substrate showing one possible mechanism of adsorption of areductant over a substrate during sequential deposition. The terms“adsorption” or “adsorb” as used herein are defined to includechemisorption, physisorption, or any attractive and/or bonding forceswhich may be at work and/or which may contribute to the bonding,reaction, adherence, or occupation of a portion of an exposed surface ofa substrate structure. During the sequential deposition technique, inaccordance with the present invention, a batch of a first processinggas, in this case “Aa_(x),” results in a layer of “A” being deposited onsubstrate 42 having a surface of ligand “a” exposed to processingchamber 37. Layer “A” may be a monolayer, more than a monolayer, or lessthan a monolayer. Thereafter, a purge gas enters processing chamber 37to purge gas “Aa_(x),” which has not been incorporated into the layer ofA. FIG. 4 is a schematic cross-sectional view of a substrate showing onepossible mechanism of adsorption of a refractory metal containingcompound over the substrate after introduction of the reductant. Afterpurging gas “Aa_(x)” from processing chamber 37, a second batch ofprocessing gas, “Bb_(y),” is introduced into processing chamber 37. The“a” ligand present on the substrate surface reacts with the “b” ligandand “B” atom, releasing molecules, for example, “ab” and “aA,” whichmove away from substrate 42 and are subsequently pumped from processingchamber 37. In this manner, a surface comprising a layer of B compoundremains upon substrate 42 and exposed to processing chamber 37, shown inFIG. 4. The composition of the layer of B compound may be a monolayer orless of atoms typically formed employing ALD techniques. In otherembodiments, more than a monolayer of B compound may be formed duringeach cycle. Alternatively, the layer of compound B may include a layerof multiple atoms (i.e., other atoms besides atoms of B). In such acase, the first batch and/or the second batch of processing gases mayinclude a mixture of process gases, each of which has atoms that wouldadhere to substrate 42. The process proceeds cycle after cycle, untilthe desired thickness is achieved.

Referring to both FIGS. 3 and 4, although any type of processing gas maybe employed, in the present example, the reductant “Aa_(x)” may compriseB₂H₆ or PH₃ and the refractory metal containing compound, Bb_(y), maycomprise WF₆. Some possible reactions are shown below in reference tochemical reaction (1) and chemical reaction (2).B₂H₆(g)+WF₆(g)→W(s)+2BF₃(g)   (1)PH₃(g)+WF₆(g)→W(s)+PF₃(g)   (2)Other by-products include but are not limited to H₂, HF or F₂. Otherreactions are also possible, such as decomposition reactions. In otherembodiments, other reductants may be used, such as SiH₄. Similarly, inother embodiments, other tungsten containing gases may be used, such asW(CO)₆.

The purge gas includes Ar, He, N₂, H₂, other suitable gases, andcombinations thereof. One or more purge gas may be used. FIG. 5 is agraphical representation of one embodiment of gases present in aprocessing chamber utilizing two purge gases Ar and N₂. Each of theprocessing gases was flowed into processing chamber 37 with a carriergas, which in this example was one of the purge gases. WF₆ is introducedwith Ar and B₂H₆ is introduced with N₂. It should be understood,however, that the purge gas may differ from the carrier gas, discussedmore fully below. One cycle of the ALD technique in accordance with thepresent invention includes flowing the purge gas, N₂, into processingchamber 37 during time t₁, which is approximately about 0.01 seconds toabout 15 seconds before B₂H₆ is flowed into processing chamber 37.During time t₂, the processing gas B₂H₆ is flowed into processingchamber 37 for a time in the range of about 0.01 seconds to about 15seconds, along with a carrier gas, which in this example is N₂. Afterabout 0.01 seconds to about 15 seconds have lapsed, the flow of B₂H₆terminates and the flow of N₂ continues during time t₃ for an additionaltime in the range of about 0.01 seconds to about 15 seconds, purging theprocessing chamber of B₂H₆. During time t₄ which lasts approximatelyabout 0 seconds to about 30 seconds, processing chamber 37 is pumped soas to remove most, if not all, gases. After pumping of process chamber37, the carrier gas Ar is introduced for a time in the range of about0.01 seconds to about 15 seconds during time t₅, after which time theprocess gas WF₆ is introduced into processing chamber 37, along with thecarrier gas Ar during time t₆. The time t₆ lasts between about 0.01seconds to about 15 seconds. The flow of the processing gas WF₆ intoprocessing chamber 37 is terminated approximately about 0.01 seconds toabout 15 seconds after it commenced. After the flow of WF₆ intoprocessing chamber 37 terminates, the flow of Ar continues for anadditional time in the range of 0.01 seconds to 15 seconds, during timet₇. Thereafter, processing chamber 37 is pumped so as to remove most, ifnot all, gases therein, during time t₈. As before, time t₈ lastsapproximately about 0 seconds to about 30 seconds, thereby concludingone cycle of the sequential deposition technique, in accordance with thepresent invention. The cycle may be repeated to deposit a tungsten layerto a desired thickness.

The benefits of employing the sequential deposition technique are manyfold, including flux-independence of layer formation that providesuniformity of deposition independent of the size of a substrate. Forexample, the measured difference of the layer uniformity and thicknessmeasured between a 200 mm substrate and a 300 mm substrate deposited inthe same chamber is negligible. This is due to the self-limitingcharacteristics of the sequential deposition techniques. Further, thistechnique contributes to improved step coverage over complex topography.

In addition, the thickness of the layer B, shown in FIG. 4, may beeasily controlled while minimizing the resistance of the same byemploying sequential deposition techniques. With reference to FIG. 6, itis seen in the slope of line 50 that the thickness of the tungsten layerB is proportional to the number of cycles employed to form the same. Theresistivity of the tungsten layer, however, is relatively independent ofthe thickness of the layer, as shown by the slope of line 52 in FIG. 7.Thus, employing sequential deposition techniques, the thickness of arefractory metal layer maybe easily controlled as a function of thecycling of the process gases introduced into the processing chamber witha negligible effect on the resistivity.

FIG. 8 is a graphical representation showing the relationship betweenthe deposition rate of a layer formed on a substrate employingsequential deposition techniques and the temperature of the substrate.Control of the deposition rate was found to be dependent upon thetemperature of substrate 42. As shown by the slope of line 54,increasing the temperature of substrate 42 increased the deposition rateof the tungsten layer B. The graph shows that less than a monolayer, amonolayer, or more than a monolayer of a tungsten layer may be formeddepending on the substrate temperature utilized. For example, at 56, thedeposition rate is shown to be approximately 2 Å/cycle at 250° C.However at point 58 the deposition rate is approximately 5 Å/cycle at atemperature of 450° C. The resistivity of the tungsten layer, however,is virtually independent of the layer thickness, as shown by the slopeof curve 59, shown in FIG. 9. As a result, the deposition rate of thetungsten layer may be controlled as a function of temperature withoutcompromising the resistivity of the same. However, it may be desirableto reduce the time necessary to deposit an entire layer of a refractorymetal.

To that end, a bulk deposition of the refractory metal layer may beincluded in the deposition process. Typically, the bulk deposition ofthe refractory metal occurs after the nucleation layer is formed in acommon processing chamber. Specifically, in the present example,nucleation of a tungsten layer occurs in chamber 12 employing thesequential deposition techniques discussed above, with substrate 42being heated in the range of about 200° C. to about 400° C., andprocessing chamber 37 being pressurized in the range of about 1 Torr toabout 10 Torr. A nucleation layer 60 of approximately about 120 Å toabout 200 Å is formed on a patterned substrate 42, shown in FIG. 10.Nucleation layers of about 100 Å or less, about 50 Å or less, or about25 Å or less have also been found to be effective in providing good stepcoverage over apertures having an aspect ratio of about 6:1 or greater.As shown, substrate 42 includes a barrier layer 61 and a patterned layerhaving a plurality of vias 63. The nucleation layer is formed adjacentto the patterned layer covering vias 63. As shown, forming nucleationlayer 60 employing ALD techniques provides good step coverage. Inanother embodiment, sequential deposition techniques may be performedfor both nucleation and bulk deposition. In still another embodiment, todecrease the time required to form a complete layer of tungsten, a bulkdeposition of tungsten onto nucleation layer 60 occurs using CVDtechniques, while substrate 42 is disposed in the same processingchamber 12, shown in FIG. 1. The bulk deposition may be performed usingrecipes well known in the art. In this manner, a tungsten layer 65providing a complete plug fill is achieved on the patterned layer withvias having aspect ratios of approximately 6:1, shown in FIG. 11.

In an alternative embodiment, a bifurcated deposition process may bepracticed in which nucleation of the refractory metal layer occurs in achamber that is different from the chamber in which the remainingportion of the refractory metal layer is formed. Specifically, in thepresent example, nucleation of a tungsten layer occurs in chamber 12employing the sequential deposition techniques, such as ALD, discussedabove. To that end, substrate 42 is heated in the range of about 200° C.to about 400° C. and chamber 37 is pressurized in the range of about 1Torr to about 10 Torr. A nucleation layer 60 of approximately 120 Å to200 Å is formed on a patterned substrate 42, shown in FIG. 10.Nucleation layers of about 100 Å or less, about 50 Å or less, or about25 Å or less have also been found to be effective in providing good stepcoverage over apertures having an aspect ratio of about 6:1 or greater.As shown, substrate 42 includes a barrier layer 61 and a patterned layerhaving a plurality of vias 63. The nucleation layer is formed adjacentto the patterned layer covering the vias 63. As shown, forming thenucleation layer 60 employing sequential deposition techniques providesimproved step coverage.

In one embodiment, sequential deposition techniques are employed forbulk deposition of tungsten onto nucleation layer 60 occurs whilesubstrate 42 is disposed in processing chamber 14, shown in FIG. 1. Thebulk deposition maybe performed using recipes disclosed herein. Inanother embodiment, CVD techniques are employed for bulk deposition oftungsten onto nucleation layer 60 occurs while substrate 42 is disposedin processing chamber 14, shown in FIG. 1. The bulk deposition maybeperformed using recipes well known in the art. Whether sequentialdeposition or CVD deposition techniques are employed, a tungsten layer65 providing a complete plug fill is achieved on the patterned layerwith vias having aspect ratios of approximately 6:1, shown in FIG. 11.Implementing the bifurcated deposition process discussed above maydecrease the time required to form a tungsten layer having improvedcharacteristics. Utilizing CVD deposition techniques for bulk depositionmay further increase throughput.

As mentioned above, in an alternate embodiment of the present invention,the carrier gas may differ from the purge gas, as shown in FIG. 12. Thepurge gas, which is introduced at time intervals t₁, t₃, t₅ and t₇,comprises Ar. The carrier gas, which is introduced at time intervals t₂and t₆, comprises of N₂. Thus, at time interval t₂ the gases introducedinto the processing chamber include a mixture of B₂H₆ and N₂, and a timeinterval t₆, the gas mixture includes WF₆ and N₂. The pump processduring time intervals t₄ and t₈ is identical to the pump processdiscussed above with respect to FIG. 5. In yet another embodiment, shownin FIG. 13, the carrier gas during time intervals t₂ and t₆ comprisesH₂, with the purge gas introduced at time intervals t₁, t₃, t₅ and t₇comprises Ar. The pump processes at time intervals t₄ and t₈ are asdiscussed above. As a result, at time interval t₂ the gas mixtureintroduced into processing chamber 37 comprises of B₂H₆ and H₂, and WF₆,and H₂ at time interval t₆.

An advantage realized by employing the H₂ carrier gas is that thestability of the tungsten layer B may be improved. Specifically, bycomparing curve 66 in FIG. 14 with curve 68 in FIG. 15, it is seen thatthe concentration of fluorine in the nucleation layer 60, shown in FIG.10, is much less when H₂ is employed as the carrier gas, as comparedwith use of N₂ or Ar as a carrier gas.

Referring to both FIGS. 14 and 15, the apex and nadir of curve 66 showthat the fluorine concentration reaches levels in excess of 1×10²¹ atomsper cubic centimeter and only as low as just below 1×10¹⁹ atoms percubic centimeter. Curve 68, however, shows that the fluorineconcentration is well below 1×10²¹ atoms per cubic centimeter at theapex and well below 1×10¹⁷ atoms per cubic centimeter at the nadir.Thus, employing H₂ as the carrier gas provides a much more stable film,e.g., the probability of fluorine diffusing into the substrate, oradjacent layer is reduced. This also reduces the resistance of therefractory metal layer by avoiding the formation of a metal fluoridethat may result from the increased fluorine concentration. Thus, thestability of the nucleation layer, as well as the resistivity of thesame, may be controlled as a function of the carrier gas employed. Thisis also true when a refractory metal layer is deposited entirelyemploying ALD techniques, i.e., without using other depositiontechniques, such as CVD.

In addition, adsorbing a layer 70, shown in FIG. 16, of either PH₃ orB₂H₆ prior to introduction of the tungsten containing compound forms atungsten layer 72 with reduced fluorine content, improved step coverage,and improved resistivity. This was found to be the case where thetungsten containing compound is introduced over a layer of PH₃ or B₂H₆employing sequential deposition techniques or employing standard CVDtechniques using either tungsten hexafluoride (WF₆) and silane (SiH₄) ortungsten hexafluoride (WF₆) and molecular hydrogen (H₂) chemistries. Theimproved characteristics of the tungsten film are believed to beattributable to the chemical affinity between the PH₃ or B₂H₆ layer andthe WF₆ layer. This provides better surface mobility of the adsorbedchemical species and better reduction of WF₆ at the nucleation stage ofthe tungsten layer. This has proven beneficial when depositing atungsten layer adjacent to a titanium containing adhesion layer formedfrom titanium (Ti) or titanium nitride (TiN). Layer 70 is preferably amonolayer, but in other embodiments may be less than or more than amonolayer. Layer 70 in the film stack, shown in FIG. 16, shows theformation of the tungsten layer 72. It is understood that layer 70 mayor may not be consumed during formation of the tungsten layer 72. It isalso understood that a plurality of layers 70 and tungsten layers 72 maybe deposited to form a tungsten layer to a desired thickness. As shown,layer 70 is deposited on substrate 74 that includes a wafer 76 that maybe formed from any material suitable for semiconductor processing, suchas silicon. One or more layers, shown as layer 74, may be present onwafer 76. Layer 78 may be formed from any suitable material, includeddielectric or conductive materials. Layer 78 includes a void 80,exposing a region 82 of wafer 76.

FIG. 18 is a detailed cross-sectional view of a substrate in which atitanium-containing adhesion layer is formed between a substrate and alayer of either PH₃ or B₂H₆ during the fabrication of a W layer adjacentto the titanium-containing adhesion layer. The titanium-containingadhesion layer may be formed employing standard CVD techniques. In oneembodiment, the titanium-containing adhesion layer is formed employingsequential deposition techniques. To that end, processing gas Aa_(x) isselected from the group including H₂, B₂H₆, SiH₄, and NH₃. Processinggas Bb_(y) is a titanium-containing gas selected from the group thatincludes TDMAT, TDEAT, and TiCl₄. Also, Ar and N₂ purge gases arepreferably employed, although other purge gas may be used.

Referring to FIGS. 2 and 17, each of the processing gases is flowed intoprocessing chamber 37 with a carrier gas, which in this example, is oneof the purge gases. It should be understood, however, that the purge gasmay differ from the carrier gas, discussed more fully below. One cycleof the sequential deposition technique, in accordance with the presentinvention, includes flowing a purge gas into processing chamber 37during time t₁ before the titanium-containing gas is flowed intoprocessing chamber 37. During time t₂, the titanium-containingprocessing gas is flowed into the processing chamber 37, along with acarrier gas. After t₂ has lapsed, the flow of titanium-containing gasterminates and the flow of the carrier gas continues during time t₃,purging the processing chamber of the titanium-containing processinggas. During time t₄, the processing chamber 37 is pumped so as to removeall gases. After pumping of process chamber 37, a carrier gas isintroduced during time t₅, after which time the reducing process gas isintroduced into the processing chamber 37 along with the carrier gas,during time t₆. The flow of the reducing process gas into processingchamber 37 is subsequently terminated. After the flow of reducingprocess gas into processing chamber 37 terminates, the flow of carriergas continues, during time t₇. Thereafter, processing chamber 37 ispumped so as to remove all gases therein, during time t₈, therebyconcluding one cycle of the sequential deposition technique inaccordance with the present invention. The aforementioned cycle isrepeated multiple times until titanium-containing layer reaches adesired thickness. For example, in reference to FIG. 18, after TiN layer84 reaches a desired thickness, layer 86, in this example formed fromPH₃ or B₂H₆, is deposited adjacent thereto employing sequentialdeposition techniques, as discussed above. Thereafter, a layer oftungsten 88, shown in FIG. 18, is disposed adjacent to layer 86 usingthe sequential deposition technique or standard CVD techniques, both ofwhich are discussed above. Layer 86 is preferably a monolayer, but inother embodiments may be less than or more than a monolayer. Layer 86 inthe film stack, shown in FIG. 18, shows the formation of the tungstenlayer 88. It is understood that layer 86 may or may not be consumedduring formation of the tungsten layer 88. It is also understood that aplurality of layers 86 and tungsten layers 88 may be deposited to form atungsten layer to a desired thickness. If desired, a copper layer maybedeposited atop of tungsten layer 88. In this manner, tungsten mayfunction as a barrier layer.

Referring again to FIG. 2, the process for depositing the tungsten layermay be controlled using a computer program product that is executed bycontroller 22. To that end, controller 22 includes a central processingunit (CPU) 90, a volatile memory, such as a random access memory (RAM)92 and permanent storage media, such as a floppy disk drive for use witha floppy diskette or hard disk drive 94. The computer program code canbe written in any conventional computer readable programming language;for example, 68000 assembly language, C, C++, Pascal, FORTRAN and thelike. Suitable program code is entered into a single file, or multiplefiles, using a conventional text editor and stored or embodied in acomputer-readable medium, such as hard disk drive 94. If the enteredcode text is in a high level language, the code is compiled and theresultant compiler code is then linked with an object code ofprecompiled WINDOWS® library routines. To execute the linked andcompiled object code, the system user invokes the object code, causingthe CPU 90 to load the code in RAM 92. The CPU 90 then reads andexecutes the code to perform the tasks identified in the program.

Although the invention has been described in terms of specificembodiments, one skilled in the art will recognize that various changesto the reaction conditions, e.g., temperature, pressure, film thicknessand the like can be substituted and are meant to be included herein.Additionally, while the bifurcated deposition process has been describedas occurring in a common system, the bulk deposition may occur in aprocessing chamber of a mainframe deposition system that is differentfrom the mainframe deposition system in which the processing chamber islocated that is employed to deposit the nucleation layer. Finally, otherrefractory metals may be deposited, in addition to tungsten, and otherdeposition techniques may be employed in lieu of CVD. For example,physical vapor deposition (PVD) techniques, or a combination of both CVDand PVD techniques may be employed. The scope of the invention shouldnot be based upon the foregoing description. Rather, the scope of theinvention should be determined based upon the claims recited herein,including the full scope of equivalents thereof.

1. A method for forming a tungsten-containing material on a substrate,comprising: positioning a substrate comprising a metal nitride barrierlayer within a process chamber; exposing the substrate to a reagent gascomprising diborane to form a reagent layer on the metal nitride barrierlayer; exposing the substrate sequentially to a tungsten precursor and areductant to form a nucleation layer thereon; and depositing a bulklayer over the nucleation layer.
 2. The method of claim 1, wherein themetal nitride barrier layer is deposited by a vapor deposition processby exposing the substrate to a reagent selected from the groupconsisting of ammonia, hydrogen, diborane, silane, derivatives thereof,and combinations thereof.
 3. The method of claim 2, wherein the metalnitride barrier layer is formed by sequentially exposing the substrateto a metal precursor and ammonia during an atomic layer depositionprocess.
 4. The method of claim 1, wherein the reductant comprises acompound selected from the group consisting of phosphine, diborane,silane, hydrogen, derivatives thereof, and combinations thereof.
 5. Themethod of claim 4, wherein the tungsten precursor comprises tungstenhexafluoride and the reductant comprises silane or diborane.
 6. Themethod of claim 5, wherein the nucleation layer has a thickness of about100 Å or less.
 7. The method of claim 1, wherein the bulk layercomprises tungsten and is deposited by a chemical vapor depositionprocess.
 8. The method of claim 7, wherein the substrate is exposed to adeposition gas comprising tungsten hexafluoride and hydrogen gas duringthe chemical vapor deposition process.
 9. The method of claim 7, whereinthe substrate is exposed to a deposition gas comprising tungstenhexafluoride and silane during the chemical vapor deposition process.10. The method of claim 7, wherein the bulk layer comprising tungstenhas a fluorine concentration of less than about 1×10¹⁷ atoms/cm³. 11.The method of claim 1, wherein the bulk layer comprises copper.
 12. Amethod for forming a tungsten-containing material on a substrate,comprising: positioning a substrate comprising at least one aperturehaving an aspect ratio of about 6 or higher within a process chamber;exposing the substrate to a reagent gas comprising diborane to form areagent layer within the at least one aperture; exposing the substratesequentially to a reductant and a tungsten precursor to form a tungstennucleation layer within the at least one aperture during an atomic layerdeposition process; and forming a tungsten bulk layer over the tungstennucleation layer to fill the at least one aperture during a chemicalvapor deposition process.
 13. The method of claim 12, wherein the atleast one aperture comprises a metal nitride barrier layer.
 14. Themethod of claim 13, wherein the metal nitride barrier layer is formed bysequentially exposing the substrate to a metal precursor and ammonia.15. The method of claim 12, wherein the reductant comprises a compoundselected from the group consisting of phosphine, diborane, silane,hydrogen, derivatives thereof, and combinations thereof.
 16. The methodof claim 15, wherein the tungsten precursor comprises tungstenhexafluoride and the reductant comprises silane or diborane.
 17. Themethod of claim 16, wherein the tungsten nucleation layer has athickness of about 100 Å or less.
 18. The method of claim 12, whereinthe tungsten bulk layer has a fluorine concentration of less than about1×10¹⁷ atoms/cm³.
 19. The method of claim 18, wherein the substrate isexposed to a deposition gas comprising tungsten hexafluoride and eitherhydrogen gas or silane during the chemical vapor deposition process. 20.A method for forming a tungsten-containing material on a substrate,comprising: positioning a substrate within a process chamber; depositinga metal nitride barrier layer on the substrate by sequentially exposingthe substrate to a metal precursor and ammonia during an atomic layerdeposition process; exposing the substrate to a reagent gas comprisingdiborane to form a reagent layer over the metal nitride barrier layer;exposing the substrate sequentially to a tungsten precursor and areductant to form a nucleation layer thereon; and depositing a tungstenbulk layer over the nucleation layer.